linux-kernel - Re: [PATCH 2/3] uprobes: __copy_insn() should ensure a

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Date:	Fri, 15 Jun 2012 14:10:31 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
Cc:	Oleg Nesterov <oleg@...hat.com>, Hugh Dickins <hughd@...gle.com>,
	Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <peterz@...radead.org>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	Anton Arapov <anton@...hat.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/3] uprobes: __copy_insn() should ensure a_ops->readpage
 != NULL


* Srikar Dronamraju <srikar@...ux.vnet.ibm.com> wrote:

> * Oleg Nesterov <oleg@...hat.com> [2012-06-07 19:00:18]:
> 
> > __copy_insn() blindly calls read_mapping_page(), this will crash
> > the kernel if ->readpage == NULL, add the necessary check. For
> > example, hugetlbfs_aops->readpage is NULL. Perhaps we should change
> > read_mapping_page() instead.
> > 
> > Signed-off-by: Oleg Nesterov <oleg@...hat.com>
> > ---
> >  kernel/events/uprobes.c |    2 ++
> >  1 files changed, 2 insertions(+), 0 deletions(-)
> > 
> > diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
> > index 48d53af..9c53bc2 100644
> > --- a/kernel/events/uprobes.c
> > +++ b/kernel/events/uprobes.c
> > @@ -616,6 +616,8 @@ __copy_insn(struct address_space *mapping, struct vm_area_struct *vma, char *ins
> > 
> >  	if (!filp)
> >  		return -EINVAL;
> > +	if (!mapping->a_ops->readpage)
> > +		return -EIO;
> 
> Nit: Should there be a blank line before the if. Ingo had insisted on
> these coding style changes.

Well, within sensible limits: if()'s can certainly be in a block 
if they do related things (such as boundary checks, etc.), so 
the above isn't ugly IMO.

Nor are separating newlines strictly necessary - it's also a 
function of the complexity of the code in question - if it's 
complex code then we want all visual and cleanliness help that 
we can think of.

Thanks,

	Ingo
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